A mineral belonging to the zeolite family of silicates. It commonly occurs in well-crystallized groupings of crystals with external rhombohedral symmetry (point group 32/m) with nearly cubic angles. This well-developed external form suggests an internal structure compatible with space group R 3m; however, one structure refinement suggests lower symmetry (triclinic) with space group P 1. In addition to recognising the distinct rhombohedral habit of chabazite crystals, the following physical properties are significant: hardness (on the Mohs hardness scale) in the range 4–5; light colours ranging from white to yellow, pink, and red; vitreous luster; and transparent to translucent in transmitted light. It is distinguished from calcite by a poorer rhombohedral cleavage and lack of effervescent reaction with dilute hydrochloric acid (HCl).